Wellheads are used in oil and gas drilling to suspend casing strings, seal the annulus between casing strings, and provide an interface with the blowout preventer (“BOP”), for example. The design of a wellhead is generally dependent upon the location of the wellhead and the characteristics of the well being drilled or produced.
In drilling the well, it is conventional to pass a number of concentric tubes (e.g., casing strings, tubing strings, etc.) down the well to support the borehole and/or segregate the borehole into annular zones. Typically, an outermost casing (i.e., conductor) is fixed in the ground, and the inner casings (e.g., casing, production casing, production tubing) are each supported from the next outer casing or by the wellhead. The wellhead is thus used to support a number of hangers that support the weight of the casing. In certain instances, it is desirable to apply torque to a downhole hanger or tool. Unfortunately, traditional torque-applying tools are typically bulky and difficult to position over the hanger, for instance. Moreover, traditional tools obstruct the borehole when installed, thus precluding full-bore access.
Hangers also use seal assemblies to seal the annuli between the hangers and the wellhead. However, the seals as well as the casing itself are subject to forces throughout the life of the well that might cause the hanger to unseat and potentially compromise the seal between the casing hanger and the wellhead, for example. Thus, the seals used with hangers must be restrained from movement when subjected to force. The seal assemblies typically include robust bodies including both inner and outer seals that are set upon by applying actuation torque from a tool above the seal assembly. Typically, because the torque is applied from above the seal assembly, the actuator tool may only access one portion of the seal assembly to apply the actuation torque. Thus, usually both the inner and outer seals of the seal assembly are set simultaneously. In some situations, however, the inner and outer seals require different amounts of force to be set and thus simultaneous actuation constrains the ability to properly form a seal against the wellhead.